1. Field of the Invention
The present invention relates to a large image display or shooting apparatus, also referred to as a retina in the case of photography.
It more particularly applies to retinas of cameras used in the detection of non-focusable radiation, such as gamma or X-rays more particularly used in the medical fields of radiology and nuclear imaging. The invention also has industrial applications, such as in particular the analysis of the state of metal parts and the production of display screens.
In the case of photography and for applications where the radiation is not focusable, it is necessary for the retina to be of the same size as the object projected by the particle source (gamma or X-rays), whereby the image can have 4,000.times.4,000 elementary elements of the retina. The known retinas used in the apparatus according to the invention have a size between approximately 1 and 16 dm.sup.2, which makes it necessary to organize several of these retinas together to obtain one large retina.
2. Description of the Related Art
An apparatus in which several of these retinas are associated is described in French patent application FR-A-2 652 655. According to the latter, the retinas used are organized in tile-like manner, i.e. they are partly superimposed.
Thus, the known image display or shooting apparatuses have a matrix of elementary elements or pixels having a sensitive surface adapted to a particular radiation (infrared, visible, X or gamma rays) or to a chosen display type.
This matrix is subdivided into an active matrix constituted by microelectronic circuits and conductive rows and columns, as well as a sensitive surface constituted by the same number of sensitive elements as there are elements in the matrix.
These sensitive elements can be smaller than the spacing of the matrix. They can also be arranged either on the same plane as the active matrix, (i.e. integrated into the latter), or on a different plane (the most frequently encountered case), when the said sensitive elements are arranged on the surface of the integrated circuit constituting the active matrix. No matter whether it is a shooting apparatus or camera, or an image display apparatus, their operation is roughly the same.
A camera has a matrix, in which each of the elementary elements comprises a sensitive element, such as a photodiode. The elementary elements of the matrixes are arranged in accordance with rows and columns, the sensitive elements being connected to microelectronic circuits and to conductive rows and columns. Under the effect of an incident radiation, the sensitive elements supply electrical signals transformed into a video signal by microelectronic circuits.
An image display apparatus or screen, receives a video signal on the inputs of microelectronic circuits, transforming the same into electrical signals applied to the sensitive elements of the screen by means of conductive columns and rows. The sensitive elements of the screen, arranged in the form of rows and columns, comprise an electrooptical material (e.g. liquid crystal), whose optical property is modified under the effect of the electrical signal applied thereto in order to permit the display of an information.
Throughout the remainder of the description particular reference will be made to a camera, knowing that the invention more particularly applies to the latter. Throughout the remainder of the text retina elementary elements, elementary points, image points or pixels are used in a random and arbitrary manner.
Moreover, the aforementioned microelectronic circuits are subdivided into conditioning circuits and addressing circuits. In the case of photography, the conditioning circuits essentially comprise, for each associated sensitive element, a switch connected on the one hand to said element by an amplifier and on the other to a conductive column and row and optionally an initialization circuit for the sensitive element. In the case of image display, these conditioning circuits essentially comprise, for each sensitive element, a switch connected on the one hand to the said element and on the other to a conductive column and line. Moreover, in the case of image display or shooting, the addressing circuits are subdivided into column addressing circuits connected to the conductive columns of the matrix and into row addressing circuits connected to the conductive rows of the matrix.
FIG. 1 shows a known matrix used in the prior art apparatus and whose operation is virtually the same as the matrixes used in the apparatus according to the invention.
For simplification reasons, the matrix shown in FIG. 1 only has a limited number, i.e. sixteen pixels, i.e. sixteen sensitive elements, each associated with a microelectronic circuit. Only a relatively brief description of said matrix will be given, because it is known.
In a more detailed form, the matrix is constituted by a sensitive area 1 having juxtaposed pixels 2 connected to conductive rows 4, conductive columns 6 and addressing circuits 12, 14. The pixels 2 are located at the intersections of the conductive rows and columns. Each pixel 2 has, in the present example, a sensitive element 10 and a conditioning circuit 8 reduced in this case to a selection switch constituted e.g. by a transistor connected to a conductive row 4, to a conductive column 6 and to said sensitive element 10.
As shown in FIG. 1, said sensitive element 10 can occupy part of the pixel surface, when it is produced in the same substrate as the conditioning and addressing circuits associated therewith, or at the most the entire pixel when the sensitive element is produced from a separate layer from that of the conditioning and addressing circuits. In the latter case, the sensitive elements are positioned above said circuits and the row and column conductors.
The transistors 8 are sequentially addressed row by row via a row addressing circuit 12 and a column addressing circuit 14. The row addressing circuit 12 selects the rows 4 in successive manner by means of a row clock 13, by raising the transistors to a given potential making it possible to make said transistors conductive.
In the case of photography, the column addressing circuit 14, for the selection time of a row, successively connects, by means of the column clock 15, the transistors 8 of said row to the matrix video output E, whilst closing the switches 18 by means of a control circuit 16 (such as a shift register) connected to the said switches. The electrical signal from the video output E therefore comes from the sensitive element 10 selected by means of the switches 18 after having been amplified by the amplifiers 20.
Therefore the column addressing circuit 14 can simultaneously collect the signals of all the sensitive elements of an addressed row. In this case, the amplifiers 20 incorporate a memory which can be sequentially read by the circuit 16.
The addressing circuits 12 and 14, integrated in the active matrix, generally occupy a 100 to 200 micron wide band on the edges of the matrix. The existence of these bands containing the addressing circuits would create shadow strips, if several such matrixes were merely juxtaposed in order to create a large screen.
The very existence of said bands has led the inventors of the previously described prior art to organize the said matrixes in a manner comparable to that of the tiles on a house roof. Thus, each matrix has addressing circuits located on one or two edges of the matrix preventing all the edges from being formed by the sensitive area. Two possibilities are then offered in the said prior art, either the arrangement of the matrixes in such a way that their sensitive areas are juxtaposed, which limits the number of matrixes to four or n.times.2 (n being the number of aligned matrixes on a row) if the addressing circuits are grouped on a single edge, or arranging the matrixes in tile-like manner.
In the latter prior art construction, the sensitive area of a matrix covers an addressing circuit of another matrix. Therefore the matrixes are assembled according to different planes and overlap one another.
This organization of the matrixes leads to the disadvantage of offering shadow areas and pixel information losses due to the thickness of the different planes of the matrixes. These shadow areas can be limited by chamfering the edge of the sensitive areas overlapping the addressing circuit, said chamfering process being very difficult and costly.